1. Field of the Invention
This invention relates to a method for making a multi-layer expanded shoe sole, more particularly to a method for making a multi-layer expanded shoe sole with a clear-cut boundary between two adjacent sole layers of the expanded shoe sole.
2. Description of the Related Art
A multi-layer shoe sole may be prepared by a conventional method involving the step of stacking and thermal molding hardened unexpanded blanks in a mold to permit the unexpanded blanks to undergo a reaction for cross-linking and expansion. However, the aforesaid method is disadvantageous in that adjacent hardened unexpanded blanks are required to have shapes which would substantially fit to each other in order to form the shoe sole with a clear-cut boundary between two adjacent sole layers of the shoe sole. As a consequence, arrangement and positioning of the adjacent hardened unexpanded blanks in the mold is inconvenient. Moreover, the bonding strength between the adjacent sole layers of the shoe sole tends to be relatively poor, and gaps may be formed between the adjacent sole layers of the shoe sole.
Therefore, the object of the present invention is to provide a method for making a multi-layer expanded shoe sole that is capable of overcoming the aforementioned drawbacks.
According to the present invention, a method for making a multi-layer expanded shoe sole comprises the steps of: (a) molding a first foamable material to form a first unexpanded blank, and cooling the first unexpanded blank to a low temperature to harden the first unexpanded blank; (b) molding a second foamable material to form a second unexpanded blank, and maintaining the second unexpanded blank at a high temperature such that the second unexpanded blank is in a softened state; and (c) stacking and thermal molding the first and second unexpanded blanks in a mold at a molding temperature to permit the first and second unexpanded blanks to undergo a reaction for cross-linking and expansion.